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Fatigue-Life Prediction Methodology Using Small-Crack TheoryThis paper reviews the capabilities of a plasticity-induced crack-closure model to predict fatigue lives of metallic materials using 'small-crack theory' for various materials and loading conditions. Crack-tip constraint factors, to account for three-dimensional state-of-stress effects, were selected to correlate large-crack growth rate data as a function of the effective-stress-intensity factor range (delta K(eff)) under constant-amplitude loading. Some modifications to the delta k(eff)-rate relations were needed in the near-threshold regime to fit measured small-crack growth rate behavior and fatigue endurance limits. The model was then used to calculate small- and large-crack growth rates, and to predict total fatigue lives, for notched and un-notched specimens made of two aluminum alloys and a steel under constant-amplitude and spectrum loading. Fatigue lives were calculated using the crack-growth relations and microstructural features like those that initiated cracks for the aluminum alloys and steel for edge-notched specimens. An equivalent-initial-flaw-size concept was used to calculate fatigue lives in other cases. Results from the tests and analyses agreed well.
Document ID
19970011006
Acquisition Source
Legacy CDMS
Document Type
Technical Memorandum (TM)
Authors
Newmann, James C., Jr. (National Aeronautics and Space Administration. Langley Research Center Hampton, VA United States)
Phillips, Edward P. (National Aeronautics and Space Administration. Langley Research Center Hampton, VA United States)
Swain, M. H. (Lockheed Martin Engineering and Sciences Co. Hampton, VA United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1997
Subject Category
Metallic Materials
Report/Patent Number
NAS 1.15:110307
NASA-TM-110307
Accession Number
97N16065
Funding Number(s)
PROJECT: RTOP 538-02-10-01
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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